Injection of water into non-cohesive subsoils fluidizes them, rendering them readily pumpable. Such subsoil overlain by a liquid medium becomes transportable by local currents upon being fluidized.
Navigable channel maintenance traditionally is attempted by dredging, repeated whenever nature fills in an existing or former channel--usually more often than anticipated. Dredging costs are so high the first time around that the necessity of periodic redredging is either not considered, or if considered is deemed an unacceptable aggravation of expense. Accordingly, in many instances no effective action is taken. Dredging itself is often so disruptive to the underwater landscape as to induce deleterious changes in currents, together with unwanted transport and redeposition of sandy subsoils.
Fluidization as a supplement or preferably as an alternative to dredging is becoming recognized, and also publicized, as by Bruun in "Maintaining Tidal Inlet Channels by Fluidization" J. Waterway, etc. Engineering, ASCE, 110 (ww4) 117-120; Bruun and Adams in "Stability of Tidal Inlets: Use of Hydraulic Pressure for Channel and Bypassing Stability" J. Coastal Research 4 (1988) 687-701; and by the present inventor with others, especially Weisman and Collins, as in "Fluidization as Applied to Sediment Transport (FAST) as an Alternative to Maintenance Dredging of Navigation Channels in Tidal Inlets" Wastes in the Ocean vol II: Dredged Material Disposal in the Ocean, Kester et al. (eds.) Wiley (1983).
Accordingly, shoals in an otherwise navigable channel or similar waterway can be relocated downstream upon being fluidized. Optionally, if natural drift at a shoal location is not favorable, but a not-too-distant region has favorable prevailing currents, the fluidized subsoil can be collected, be pumped to, and be released at the latter location for natural redistribution. Another option or related variation is suggested by Lin in U.S. Pat. No. 4,898,495. As the physical characteristics and behavior of non-cohesive subsoils become better understood, fluidization doubtless will be recognized as the procedure of choice, both technically and economically, to solve such environmental problems as shoaling of navigable channels.
Underwater collection of fluidized subsoil is essential to the more active redistribution according to the second and third of the foregoing options. My present invention is directed mainly toward modifying fluidization of non-cohesive subsoils so as to facilitate their redistribution, and especially to their underwater collection.